Heart valve prosthesis

ABSTRACT

A &#34;tissue valve type&#34; heart valve prosthesis is disclosed which has a biocompatible plastic sewing ring adapted to be surgically implanted into the mitral, aortic or tricuspid annulus of the human heart. The sewing ring has internal square threads and a biocompatible fabric mesh or cloth is embedded into the sewing ring so that the cloth can be fully wrapped around the sewing ring covering all of its plastic surfaces except for the internally protruding threads. A biocompatible plastic stent support ring has externally disposed threads to lock with the threads of the sewing ring in approximately one turn, or less. The stent support ring also embeds a biocompatible fabric mesh which can be wrapped around the stent support ring to cover all of its plastic surfaces, except for the protruding threads, and to form a cloth pocket wherein a solid stent is mounted. A porcine trileaflet valve is mounted to the stent. When the heart valve prosthesis is as implanted into the heart, the threads of the sewing ring and of the stent support ring interlock, and there are no plastic or metal surfaces, uncovered by biocompatile fabric, to be exposed to blood flow. Processes for making the solid metal stent by laser cutting, and the sewing and stent support rings by a specifically adapted plastic molding procedure, are also disclosed.

This is a divisional of co-pending application Ser. No. 664,150, filedon Oct. 24, 1984 which is now U.S. Pat. No. 4,680,031, which is acontinuation-in-part of Ser. No. 445,259, filed on Nov. 29, 1982, nowabandoned, which is a continuation-in-part of Ser. No. 303,345, filed onOct. 7, 1982, now abandoned. BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention is in the field of heart valve implantations. Moreparticularly, the present invention is directed to artficial heartvalves of the type which include a sewing ring to be permanentlyinstalled in the heart, and a tissue valve mounted to a stent removablyattachable to the sewing ring.

2. Brief Description of the Prior Art

Two major types of heart valve implantations are known in the prior art.One of these, includes a metal or plastic artificial valve structurewhich regulates the direction of the blood flow in the anatomicalstructure wherein the heart valve is incorporated. By their very nature,these "mechanical type" heart valves have metal or plastic surfacesexposed to the blood flow, which remain thrombogenic even long timeafter their implantation by major surgery. Therefore, patients wearingsuch "mechanical type" heart valves can avoid potentially lifethreatening embolus formation only by constantly takinganti-thrombogenic medication, such as cumadine.

Another major type of artificial heart valve implant utilizes a tissuevalve of animal (principally porcine) origin to regulate the directionof blood flow. Such porcine "tissue valves" include three cusps orleaves of a heart valve excised from pigs and preserved by treatmentwith glutaraldehyde. The animal tissue portion of the artificial "tissuevalves" is, generally speaking, not thrombogenic. Therefore, at leastsome time after the surgical implantation of the artificial "tissuevalves", the human patient would not necessarily requireanti-thrombogenic medication (cumadine), unless, of course, some otherportion of the artificial valve implantation includes thrombogenic metalor plastic surfaces exposed to the blood flow. Therefore, designers ofthe tissue valve type heart valve implants have, generally speaking,strived to minimize the plastic and metal surfaces of artificial heartvalves which are exposed to blood flow.

Another important goal of artifical heart valve design is to minimizeobstruction of blood flow in the anatomical structure wherein theartificial valve is implanted, i.e. to maximize the unobstructed flowpassage area in the mitral, aortic or tricuspid annulus wherein theartificial valve is surgically mounted.

Still another goal is to render the "working" (flow directionregulating) valve structure replaceable without the need for surgicallyremoving and destroying heart tissue in the annulus where the valveimplant is mounted by sutures.

In efforts to attain the above-noted and related goals, the prior arthas provided artificial heart valve implants which include a sewing ringand a valve structure removably mountable to the sewing ring. The sewingring is, usually, a short section of a tube which is attached to asuitable biocompatible cloth or fabric. The sewing ring is surgicallysewn (sutured) to the heart tissue.

The remainder of the artificial heart valve implant, whether it is the"mechanical" or "tissue valve" type, usually includes a supportstructure for the valve mechanism, with the support structure beingsecurable by some type of locking mechanism to the sewing ring. Thelocking mechanism include threads in the sewing ring and complementarythreads in the support structure. In addition to the foregoing, theprior art has also provided heart valve implants of the type wherein thesewing ring is integral (i.e. not removable during surgery), with therest of the valve structure.

The valve support structure of the removable (and also non removable)tissue valve type heart valve implants usually includes a stent. Thestents of the prior art usually comprise a bent wire structure made of abiocompatible, non-corrosive metal, such as stainless steel, orpreferably a cobalt - nickel alloy known under the ELGILOY trade name.The stent typically includes a circular base and three stent posts(commissural posts) configured in such a manner that the three cusps ofthe porcine tissue heart valve can be attached to and are operativelysupported by the commissural posts. In some prior art artificial valveimplants, the stent is covered by a porous biocompatible fabric or clothinto which human tissue in-growth can occur after implantation, so as toreduce the risk of potentially dangerous blood clot formation.

Specific examples of prior art artifical heart valve implants are foundin U.S. Pat. Nos. 3,744,062; 3,835,475; 3,997,923; 4,364,126 and4,106,129. U.S. Pat. Nos. 4,211,325; 4,319,363 and 4,257,444 disclosesubject matter which is of general background interest to the presentinvention.

The above-summarized prior art heart valves, including those disclosedin the above-cited patents, generally speaking, suffer from thefollowing disadvantages. Plastic or metal surfaces of the valve implantsremain exposed to the blood flow even in the "tissue valves" of theprior art, so that the patient wearing the valve implant must depend onanti-thrombogenic medication in order to avoid potentially lethal bloodclot formation.

The configuration of the wire stent is often less than optimal for themounting and prolonged functioning of the trileaflet (three-cusp)porcine valve. In addition, bent wire made of stainless steel, andparticularly of cobalt - nickel alloy (ELGILOY), is not ideally suitedfor forming the stent from a structural integrity standpoint, eventhough ELGILOY is quite satisfactory from the standpoint of corrosionresistsance and biocompatibility. This is because, in order to provideadequate strength the wire must be fairly thick, and the thickness ofthe wire substantially reduces the flow-through area in the annuluswherein the valve implant is mounted. Moreover, in order to provide thenecessary commissural posts in the stent, the wire of the stent must besubjected to relatively sharp bends which adversely affect itsstructural integrity. In this regard it is noted that for the making ofcertain stents for tissue valves, ELGILOY wire must be bent to a greaterextent than what is considered acceptable by the manufacturers of thewire.

Still further, in the prior art heart valve prostheses which have a bentwire stent, an additional plastic support member must be mounted in thestent to operatively support the trileaflet porcine tissue valve. Theneed for this additional support member, of course, complicates theassembly of the heart valve prosthesis, and increases its cost.

Finally, the process of mounting the stent bearing the tissue valve, (ormechanical valve) to the sewing ring is difficult because of theconditions prevailing during open heart surgery, regardless of thestructure of the valve implant. The prior art valve implants which hadrelatively complex mounting mechanisms have, generally speaking,rendered the task of the surgeon more difficult than desirable andexposed the patient to high risk.

In light of the foregoing, there is a genuine need in the prior art forimproved artifical heart valve designs which overcome the above-noteddisadvantages. The present invention provides such artificial heartvalve designs.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide an artificial heartvalve implant of the "tissue valve" type which contains virtually nometal or plastic surfaces exposed to the blood flow, whereby the patientwearing the implant does not require continuous anti-thrombogenicmedication.

It is another object of the present invention to provide an artificalheart valve implant which is designed to maximize the area available forblood flow in the mitral, aortic or tricuspid annulus where the implantis surgically mounted.

It is still another object of the present invention to provide anartificial heart valve implant wherein the stent supporting the valvestructure is not subjected to undue bending stresses which adverselyaffect its structural integrity.

It is yet another object of the present invention to provide anartificial heart valve implant of the type having a sewing ringpermanently attachable to the human heart, and a valve structureremovably attachable to the sewing ring, wherein mounting and demountingof the valve structure to the sewing ring can be readily performed underthe conditions of open heart surgery.

The foregoing and other objects and advantages are attained by anartificial heart valve implant which has a sewing ring having interiorthreads, and a stent support ring having exterior threads so that thestent support ring is threadably mountable into the sewing ring. Thesewing ring and the stent support ring are made of biocompatiblethermoplastic material. Preferably, the threads are square threads ofthe type which lock the sewing ring and the stent support ring to oneanother in less than one turn.

A first cloth of a biocompatible fabric mesh is embedded in the sewingring so that the internal threads of the sewing ring and the exteriorwall of the sewing ring are disposed on different sides of the firstcloth. The first cloth is folded over the external wall of the sewingring to form a cloth ring which is adapted to be secured by sutures intothe mitral, aortic or tricuspid annulus in the human heart.

A second cloth of biocompatible fabric mesh is embedded in the stentsupport ring in an analogous manner, and the second cloth is folded overthe internal, non-threaded wall of the stent support ring to provide acloth pocket into which a metal stent of the heart valve prosthesis ismounted to fully enclose the stent in the cloth. Preferably, inaccordance with the present invention, the stent is a substantiallysolid tubular metal member, which has a plurality of apertures to permitaffixation of the cloth to the stent.

The sewing ring and the stent support ring are manufactured integrallywith the respective cloth of fabric in a plastic molding process. Thisprocess comprises a separate aspect of the present invention. In theprocess, the cloth is first placed in a mold and molten plastic isinjected under high pressure to flow through a portion of the cloth andto form the sewing ring and stent support ring, respectively, integralwith the cloth.

The features of the present invention together with further objects andadvantages, can be best understood from the following description, takentogether wih the appended drawings, wherein like numerals indicate likeparts.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view showing the four major components of theheart valve prosthesis of the present invention, before the componentsare assembled to one another;

FIG. 2 is a perspective view showing a cloth covered sewing ring, stentand stent support ring of a mitral heart valve prosthesis in accordancewith the present invention;

FIG. 3 is a perspective view of the components shown on FIG. 2, saidcomponents having been assembled to one another;

FIG. 4 is a perspective view showing a cloth covered sewing ring, stentand stent support ring of an aortic heart valve prosthesis in accordancewith the present invention;

FIG. 5 is a perspective view of the components shown on FIG. 4, saidcomponents having been assembled to one another;

FIG. 6 is a cross-sectional view taken on lines 6,6 of FIG. 2;

FIG. 7 is a cross-sectional view taken on lines 7,7 of FIG. 4;

FIG. 8 is a cross-sectional view taken on lines 8,8 of FIG. 2;

FIG. 9 is a cross-sectional view taken on lines 9,9 of FIG. 3;

FIG. 10 is a cross-sectional view taken on lines 10,10 of FIG. 5;

FIG. 11 is a top view of a flat plate intermediate used in thefabrication of a preferred embodiment of the stent of the presentinvention;

FIG. 12 is a perspective view of another intermediate in the process offabricating the stent of the present invention;

FIG. 13 is a perspective view of the preferred embodiment of the stentof the present invention;

FIG. 14 is a cross-sectional view of the stent shown on FIG. 13, theview being taken on lines 14,14 of FIG. 13;

FIG. 15 is a cross-sectional view of a mold used in the process offabricating the novel sewing ring of the present invention;

FIG. 16 is a partial plan view taken on lines 16,16 of FIG. 15;

FIG. 17 is a partial plan view taken on lines 17,17 of FIG. 15;

FIG. 18 is a cross-sectional view of a mold used in the process offabricating the novel stent support ring of the present invention, and

FIG. 19 is a partial plan view taken on lines 19,19 of FIG. 18.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The following specification taken in conjunction with the drawings setsforth the preferred embodiment of the present invention. The embodimentof the invention disclosed herein is the best mode contemplated by theinventor for carrying out his invention in a commercial environment,although it should be understood that various modifications can beaccomplished within the parameters of the present invention.

Referring now to the drawing Figures, the preferred embodiments of theheart valve prostheses of the present invention are disclosed. It shouldbe noted at the outset in this regard that mitral, aortic and tricuspidheart valve prostheses of various sizes can be fabricated by applyingthe generic principles and teachings of the present invention which aredisclosed below. Moreover, the glutaraldehyde preserved porcine tissuevalves which are incorporated in the heart valve prostheses of thepresent invention for regulating the direction of blood flow in theprostheses, are well known in the art. Therefore, for the sake oflucidity of the appended drawings, the porcine tissue valve is shownonly schematically and only on FIG. 1. It should also be remembered thatcertain generic principles of the invention disclosed herein are alsoapplicable for the construction of mechanical type heart valves, andeven for the construction of other types of implantation devices.

Referring now to FIG. 1, the four major components of the heart valveprostheses of the present invention are shown before the components areassembled to one another. The four components are: a sewing ring 30, astent 32, a stent support ring 34 and the porcine tissue valve 36. Amongthese components, the porcine tissue valve 36 is standard (as notedabove), and is described in the present specification only to the extentnecessary to disclose its relationship to the other novel components.

The novel sewing ring 30, and stent support ring 34 of the heart valveprostheses of the present invention are best explained with reference toFIGS. 2 through 10. Among these, FIGS. 2, 3, 6, 8 and 9 illustrate amitral heart valve prosthesis (without showing the porcine tissue valve36), and FIGS. 4, 5 7 and 10 illustrate an aortic heart valve prosthesis(also without showing the porcine tissue valve 36).

The sewing ring 30 is a relatively short tube section made of abiocompatible thermoplastic material, such as polypropylene, polyacetateor polycarbonate. It includes a first cloth tube 38, square threads 40in its interior, and a smooth exterior wall 42.

A principal novel feature of the sewing ring 30 is that it embeds thefirst cloth tube 38 in the manner illustrated in the drawing Figures, sothat the interior threads 40 of the sewing ring 30 are disposed withinthe interior 44 of the first cloth tube 38 and the exterior wall 42 ofthe sewing ring 30 is disposed on the exterior 46 of the first clothtube 38. Thus, the first cloth tube 38 is integrally constructed withthe plastic body 48 of the sewing ring 30.

For the fabrication of a sewing ring 30 for a mitral heart valveprosthesis, the first cloth tube 38 is folded over the external wall 42of the sewing ring 30 to fully enclose the plastic body 48 of the sewingring 30, except for the internally protruding threads 40. As is bestshown on the cross-sectional views of FIGS. 6 and 9, the first clothtube 38 is also folded over itself and is secured with stitches 50 tocapture a suitable elastic member 52, which is made of a biologicallycompatible rubber or like material. This structure provides a paddedcloth ring 54 which is substantially concentrical with the plastic body48 of the sewing ring 30. In this regard it is noted that FIG. 1illustrates the sewing ring 30 as an intermediate, having the embeddedfirst cloth tube 38, before the cloth tube 38 is folded, trimmed andstitched to capture the elastic member 52.

For the fabrication of a sewing ring 30 for an aortic heart valveprosthesis in accordance with present invention, essentially the samesteps of folding the first cloth tube 38, and trimming and stitching thesame are followed. For essentially anatomical reasons, which are wellunderstood by those skilled in the art, the cloth ring 54 of an aorticheart valve prosthesis, however, does not incorporate an elastic member.The structure, of the sewing ring 30 of an aortic heart valve prosthesisof the present invention is best shown on the cross-sectional views ofFIGS. 7 and 10.

The stent support ring 34 of the heart valve prostheses of the presentinvention is best shown on FIGS. 8, 9 10. Thus the stent support ring 34also includes a plastic body 56 which has exterior square threads 58,and an interior wall 60. A second cloth tube 62 is embedded in theplastic body 56 of the stent support ring 34 in such a manner that theexterior threads 58 of the stent support ring 34 are disposed on theexterior 64 of the second cloth tube 62, and the interior wall 60 of thestent support ring 34 is disposed within the interior 66 of the secondcloth tube 62. The dimensions and configuration of the stent supportring 34 is selected in such a manner that the stent support ring 34 isthreadably mountable to the sewing ring 30, as is shown on FIGS. 3, 5, 9and 10.

In order to assemble the stent 32 to the stent support ring 34 for theheart valve prostheses fabricated in accordance with the presentinvention, the second cloth tube 62 is folded over the interior wall 60of the stent support ring 34. In this manner, the stent support ring 34is fully enclosed in the second cloth tube 62 and a cloth pocket 67 isformed wherein the stent 32 is mounted by sewing and stitches 50.

It should be apparent from the foregoing description and from inspectionof the drawing Figures, that the first cloth tube 38 and the secondcloth tube 62 are embedded in the threads 40 and 58 of the respectiverings 30 and 34, in the sense that the cloth tubes form the valleys ofthe threads. This is an important advantage over prior art sewing ringsand stent support rings because the embedded cloth is more securelyattached to the rings than if the cloth were attached merely byadhesives (not shown), rivets (not shown) or like mechanical fasteners.In addition, in some prior art heart valve prosthesis cloth is placedover the threads before fastening. This is clearly not necessary in theheart valve prosthesis of the present invention.

Moreover, it should be apparent from the foregoing, that the stentsupport ring 34 bearing the untrimmed second cloth tube 62, as isillustrated in FIG. 1, is merely an intermediate in the fabrication ofthe final form of the stent support ring 34 which is incorporated in theheart valve prostheses of the present invention.

The first and second cloth tubes 38 and 62 embedded in the sewing andstent support rings 30 and 34 of the heart valve prostheses of thepresent invention, comprise a fabric mesh of a biocompatible plasticmaterial, preferably polyester (polyacetate) fabric. The use of suchfabric mesh to enclose various plastic and metal members which aresubsequently surgically implanted in the human body, is, per se, knownin the art. As is well known, after implantation into the human body, aningrowth of collageneous tissue usually forms in the interstitial spacesof the fabric, and endothelial cells cover the fabric to provide anon-thrombogenic autologous surface. Therefore, at least sometime afterthe implantation, the cloth covered plastic or metal members no longercause coagulation of blood, and present no significant danger of embolusformation when implanted in the heart. The fabric mesh or cloth of thefirst and second cloth tubes, as similar fabric used in the art, isrelatively thin, preferably it is approximately 0.3 mm thick.

Referring now principally to FIGS. 1, and 13, the stent 32 incorporatedin the heart valve prostheses of the present invention is described. Thestent 32 of the present invention is a substantially tubular memberformed from a substantially solid, thin plate 68 of a biocompatiblemetal, such as stainless steel or a cobalt - nickel alloy. Preferably,the stent 32 is formed from a substantially solid plate 68 of theproprietary cobalt-nickel alloy known under the ELGILOY trade mark.

The stent 32 incorporates three commissural posts 70 which areconfigured for optimal support of the three cusps 72 of the trileafletporcine tissue valve 36. A plurality of relatively small round holes orapertures 74 are disposed in the stent 32. The holes 74 accept stitches50 whereby the fabric mesh of the second cloth tube 62 is sewn toenclose the stent 32. This is well illustrated in FIGS. 2, 3, 4, and 5.

A principal novel feature of the stent 32 is that it is made of a solidplate 76, rather than of bent metal wire (not shown). This isadvantageous because the solid stent 32 of the present invention has noundue structural strain caused by excessive bending (as in prior artbent wire stents), and is made from significantly thinner (approximatelyten times thinner) metal plate than the wire (not shown) of prior artwire stents (not shown). The plate 76 of the stent 32 of the presentinvention is typically and approximately 0.005 to 0.010 inch thick.Instead of the round holes 74, slots (not shown) or like equivalents ofholes, may also be used in the stent 32 to accept the stitches 50. Aprocess for fabricating the stent 32 of the present invention isdescribed below.

Referring now again principally to FIGS. 3, 5, 9, and 10, the stent 32is shown affixed in the cloth pocket 67 formed from the second clothtube 62 which is itself embedded in the stent support ring 34. Thesefigures also show the stent 32 and stent support ring 34 mounted to thesewing ring 30, as the structure is assembled after implantation in theheart (not shown). As it was noted above, the porcine tissue valve 36,which is mounted by stitches 50 to the cloth covering of the stent 32,is omitted from the drawing Figures for simplicity of illustration. Ashoulder or lip 78 is incorporated into the plastic body 48 of thesewing ring 30 to set the limit how far the stent support ring 34 can bethreaded into the sewing ring 30.

The manner of surgically implanting the novel heart valve prostheses ofthe present invention should be readily apparent from the foregoingdescription. Thus, the surgeon (not shown) first implants the sewingring 30 into the mitral, aortic or tricuspid annulus (not shown).Therafter, the stent support ring 34 which bears the stent 32 and theporcine tissue valve 36, is threadably mounted into the sewing ring 30.The square threads 40 of the sewing ring 30 readily engage the likethreads 58 of the stent support ring 34 within approximately one turn orless. The pressure of the stent support ring 34 on the lip 78 locks thestent support ring 34 into operative position in the sewing ring 30. Ifthe heart valve prosthesis must be replaced at a later time, for examplebecause of calcification of the porcine trileaflet valve 36, thenremoval of the stent support ring 34 from the sewing ring 30 isrelatively easy because the square threads readily separate from oneanother. It should be readily apparent from the foregoing that thesewing ring 30 of the heart valve prosthesis of the present inventiondoes not need to be replaced to replace a defective porcine tissue valve36.

An inspection of the drawing Figures, principallly of FIGS. 9 and 10,reveals that there are no exposed plastic or metal surfaces in the heartvalve prosthesis of the present invention. Thus, at least sometime afterthe implantation of the heart valve prosthesis of the present invention,the patient (not shown) may be gradually taken off anti-thrombogenicmedication. This is because, as soon as the cloth enclosing theprosthesis is covered by human tissue, there are no exposed thrombogenicsurfaces in the prosthesis and no further danger of embolus formation.

In alternative preferred embodiments of the heart valve prostheses ofthe present invention, the cloth covering the prosthesis may be coated,before implantation, with collagen fibers reconstituted from purifiednatural collagen and cross linked by the NH₂ groups to the underlyingpolyester fabric. Additional coatings of this "artificial" collagenlayer with mucopolysacharides and/or proteins is also possible. Theforegoing reduce the thrombogenecity of the implant at the time ofimplantation.

It should also be readily appreciated by those skilled in the art, thatthe thin stent 32 used in the heart valve prosthesis of the presentinvention results in a larger flow-through area in the mitral, aortic ortricuspid annulus (not shown), than would be possible with prior artprostheses having substantially thicker wire and/or plastic stents (notshown). For some patients, particularly for those with weak heart musclefunction, the foregoing advantage may provide the ability to performcertain vigorous physical activities, which might not be possible withprostheses having the prior art wire and/or plastic stents (not shown).

Referring now to FIGS. 11 through 14, the process of making the novelstent 32 of the present invention is disclosed. A flat plate 76 of theshape shown in FIG. 11, is formed first by laser cutting, electrodedischarge machining, electron beam machining, stamping or chemicaletching, with laser cutting being preferred. The plate 76 is made ofstainless steel, or preferably ELGILOY, and is approximately 0.005 to0.010 inch thick. The apertures 74, or in alternative embodiments, slots(not shown), are also preferably laser cut into the plate 76.

The flat plate 76, having substantially the shape shown on FIG. 11 isthereafter bent by passing through suitable rollers (not shown) into theconfiguration shown in FIG. 12. The bending of the plate 76 is uniformthrough the whole body of the plate 76, so that no sharp bends or unduestresses arise in the plate 76. Two, preferably obliquely cut, edges 80of the plate 76 are then brought into contact with one another, as shownon FIG. 12, and the plate 76 is secured into its final tubularconfiguration by resistance welding a small fastener plate 82 within itsinterior. This is shown on FIGS. 13 and 14.

After the step of welding, sharp edges of the intermediate stent 32 areremoved by tumbling the intermediate for several hours, (preferablyapproximately 24 hours) with aluminum oxide (Al₂ O₃) rocks, or likeabrasive material. The resulting stent 32, is sewn into the cloth pocket67 embedded in the stent support ring 32, as it was described above indetail.

Referring now to FIGS. 15 through 19, the process of making the novelsewing ring 30 and stent support ring 34 of the present invention isdisclosed. The hereinbelow described process is actually suitable formaking various plastic surgical implant and other items which must havea fabric securely fastened to the plastic body of the item. Therefore,in this respect the invention is broader than the fabrication ofcomponents for heart valve prosthesis. Nevertheless, the process isillustrated hereinbelow by the specific example of the preparation ofthe sewing ring 30 and stent support ring 34 of the heart valveprosthesis of the present invention.

Thus, a die or mold 84 specifically adapted for the making of the sewingring 30 is shown schematically on FIG. 15. The mold 84 has suitablecavities 86 where the excess of the first cloth tube 38 is accomodated.A mandrel 88 fixedly attached to a bottom piece 90 of the mold 84 hascavities 92 which correspond to the shape of the interior threads 40 ofthe sewing ring 30. A plurality of ducts 94 are incorporated in the mold84 to permit liquid plastic (not shown) to flow to the mandrel 88. Acylindrical mold piece 96 is disposed on top of the mandrel 88.

For assembly of the mold 84, the first cloth tube 38 is first placed onthe mandrel 88 and the cylindrical mold piece 96. Thereafter, the mold84 is assembled with intermediate pieces 98, 100 and 102, substantiallyas shown on FIG. 15. The assembled mold 84, incorporating the firstcloth tube 38 is preferably preheated. Thereafter, molten thermoplastic(not shown) is injected into the mold 84 under pressure to cause themolten plastic (not shown) to flow through the ducts 94 to and throughthe cloth 38 into the cavities 92 formed by the mandrel 88 and theadjacent mold pieces 98 and 100. In the herein disclosed preferredembodiment of the mold 84, the intermediate pieces 98, 100 and 102 whichsurround the cloth tube 38, are formed from two complementary piecesheld together by bolts or the like (not shown). After cooling, the mold84 is disassembled to provide the sewing ring 30 integral with the firstcloth tube 38.

FIGS. 18 and 19 depict a mold 104 for the making of the stent supportring 34. Description of this mold 104 is not considered necessary here,since it construction and operation can be readily understood from thedescription of the mold 84 which is used for making the sewing ring 30.

Those skilled in the art of plastic molding, and in the related medicaltechnological arts will readily recognize that several modifications ofthe molds 84 and 104 and of the hereinbelow described specific processparameters are possible to make the novel composite fabric and plasticitems of the invention. Therefore, the ensuing description of thespecific parameters of the molding process should be consideredexamplary rather than limiting in nature.

Thus, the molds 84 and 104 are preferably made of aluminum. Biologicallyimplantable polyester (DACRON) cloth woven in the shape of a tube isplaced into the mold 84, or the mold 104. The mold is then preheated toapproximately 180 Fahrenheit. The mold is used in a Morgan injectionmachine, wherein biologically implantable polyacetal (Dupont, DELRIN)plastic is heated to approximately 425 to 450 Fahrenheit. The melt isinjected into the mold at approximately 4000 PSI pressure. After themold is sufficiently cooled, it is disassembled to provide the compositeplastic cloth sewing ring 30, or stent support ring 34.

Several modifications of the above described novel heart valveprostheses and of the associated part and processes may become readilyapparent to those skilled in the art in light of the above disclosure.Therefore, the scope of the present invention should be interpretedsolely from the following claims.

What is claimed is:
 1. A method of fabrication of a stent for anartificial heart valve comprising:cutting a plate of metal having athickness of 0.010 inches or less to produce an elongated stent memberhaving a first end, a second end, a lower edge, and an upper edge, saidupper edge provided with three commissural posts extending therefrom;bending said stent member to place said first end adjacent said secondend of said stent member; and mechanically coupling said first end tosaid second end of said stent member.
 2. A method according to claim 1wherein said step of bending said stent member to bring said first endadjacent to said second end further comprises the step of passing saidstent member through rollers to impart a uniform bend to the stentmember from said first end of said stent member to said second end ofsaid stent member.
 3. A method according to claim 1 wherein said step ofmechanically coupling said first end of said stent member to said secondend of said stent member comprises welding.
 4. A method of fabricating astent for an artificial heart valve comprising cutting a metal platehaving a thickness of about 0.005 to 0.010 inches to produce anelongated stent member having a first end, a second end, a lower edge,and an upper edge, and having three commissural posts extending fromsaid upper edge;bending said stent member to place said first end ofsaid stent member adjacent said second end of said stent member suchthat said stent member assumes a generally tubular configuration; andmechanically coupling said first end of said stent member to said secondend of said stent member.
 5. A method according to claim 1, 2, 3 or 4wherein said cutting step comprises cutting said stent member from asheet of Elgiloy.
 6. A method according to claim 1, 2, 3, or 4 whereinsaid cutting step comprises cutting said stent member from a sheet ofstainless steel.